Linear pumping system and methods for controlling the same

ABSTRACT

An example linear pumping system suitable for small size and low flow rate operation. The system includes a pump casing that encloses a linear motor and one or two (an upper and lower) pumps. The pump casing may include an upper fluid inlet port, a lower fluid inlet port, and a fluid-outlet port. The linear motor includes a stator and a mover, where the mover includes an upper plunger portion and a lower plunger portion and is configured to move alternately up and down relative to the stator. The upper and lower pumps positioned on both sides of the mover may each include a pump chamber, a fluid inlet valve, and a fluid outlet valve. In operation, hydraulic pressure from the upper and lower pump outlet valves causes fluid within an interior cavity of the pump casing to be expelled through the fluid outlet port. The motion of the mover can be controlled using pressure and/or plunger position measurements.

FIELD

The technology described herein relates generally to a linear pumpingsystem, and more particularly to systems and methods for pumping fluidsfrom an oil or gas well.

BACKGROUND

The oil and gas industry relies heavily on pumping systems with seventypercent or more of the world's oil wells requiring some sort of a pumpto produce fluids. Linear pump technology is the most commonly used pumptechnology in the oil industry. More specifically, the most common typeof pumps used in wells having a low flow rate or a small well bore sizeand also with gas wells is the sucker rod driven linear pump. However,sucker rod driven linear pumps are typically not efficient at low flowrates because their slow operation and large pump size requires a verylarge amount of force to lift fluid, even at a low flow rate. Thesepumps may also have other disadvantages, such as a moving rod seal onthe well head that is prone to leaking, and operating poorly in thepresence of gas, as well as a pumping chamber that cannot be strokeduntil empty because the plunger is on the end of a long rod string, manythousands of feet long. There is therefore a need in the industry for asystem for pumping fluids from an oil or gas well that operatesefficiently at low flow rates and addresses disadvantages associatedwith the prior art.

SUMMARY

An example linear pumping system and methods of operation are provided.An example linear pumping system may include a pump casing that enclosesa linear motor and one or preferably two pumps designated herein forconvenience upper and lower pump. In an embodiment, the pump casingincludes an upper fluid inlet port, a lower fluid inlet port, and afluid-outlet port. The linear motor includes a stator and a mover, wherethe mover may include an upper plunger portion and a lower plungerportion and is configured to move alternately up and down relative tothe stator when the motor is powered up. In embodiments, the upper pumpmay include an upper pump chamber, an upper pump fluid inlet valve, andan upper pump fluid outlet valve, and the lower pump may include a lowerpump chamber, a lower pump fluid inlet valve, and a lower pump fluidoutlet valve. In operation, hydraulic pressure from the upper and lowerpump outlet valves causes fluid within an interior cavity of the pumpcasing to be expelled through the fluid outlet port of the pump casing.

In embodiments, an upper pump fluid inlet valve may be provided betweenthe upper pump chamber and the upper fluid inlet port and is configuredto receive fluid into the upper pump chamber from outside of the pumpcasing. An upper pump fluid outlet valve may be provided between theupper pump chamber and an interior cavity of the pump casing and isconfigured to expel fluid from the upper pump chamber into the interiorcavity of the pump casing. The upper pump chamber may be configured toreceive the upper plunger portion of the linear motor mover, where theupper plunger portion causes fluid to be drawn into the upper pumpchamber through the upper pump inlet valve on a downstroke of the linearmotor mover and causes fluid to be expelled from the upper pump chamberthrough the upper pump outlet valve on an upstroke of the linear motormover.

In embodiments, a lower pump fluid inlet valve may be provided betweenthe lower pump chamber and the lower fluid inlet port and is configuredto receive fluid into the lower pump chamber from outside of the pumpcasing. A lower pump fluid outlet valve may be provided between thelower pump chamber and the interior cavity of the pump casing andconfigured to expel fluid from the lower pump chamber into the interiorcavity of the pump casing. The lower pump chamber may be configured toreceive the lower plunger portion of the linear motor mover, where thelower plunger portion causes fluid to be drawn into the lower pumpchamber through the lower pump inlet valve on the upstroke of the linearmotor mover and causes fluid to be expelled from the lower pump chamberthrough the lower pump outlet valve on the downstroke of the linearmotor mover.

An example method of controlling operation of a linear pumping systemfor use in an oil or gas well, where the linear pumping system includesa linear motor and one or more pump chambers, may include the steps of:measuring pressure within the one or more pump chambers of the linearpumping system; measuring a position of a plunger rod of the linearmotor in relation to the one or more pump chambers; and controllingmovement of the plunger rod within the one or more pump chambers basedat least in part on the measured pressure and/or position. Inembodiments, a stroke length of the linear motor may be controlled basedat least in part on the measured position of the plunger rod to cause amaximum penetration of the plunger rod within the one or more pumpchambers. In embodiments, movement of the linear motor may be stopped ifthe measured pressure exceeds a predetermined threshold. Example methodsof controlling operation of a linear pumping system for use in an oil orgas well may further include the steps of measuring an operationaltemperature of the linear motor; and controlling movement of the linearmotor based at least in part on the measured operational temperature. Inembodiments, movement of the linear motor may be stopped if the measuredoperational temperature exceeds a predetermined threshold.

The invention is described as advantageously having two pumpingchambers, one on either end of the linear motor. This arrangementprovides several advantages over other arrangements, principallybalanced forces on the motor and near continuous pumping. However itshould be noted that this pump arrangement also provides redundancy, andthat if one pumping chamber fails the second one may continue tooperate, providing some failure tolerance. It is also true that in avertical well bore one can observe what is known as a pump-off. Pump-offis a phenomenon occurring when pumping action draws the fluid columndown below the pump intake. A pump-off situation will significantlyincrease the gas intake, reducing the pump efficiency. Thus, if thesurrounding fluid level gradually drops (pumping off) the upper chamberwill draw gas (or gassy fluids) before the lower chamber, and so thepump described herein should not pump off suddenly. This asymmetricbehavior of the pump will be an indication to the control system of apump off condition, and will provide the mechanism to control pumpingunder such common conditions. This is an additional advantage of thepump design disclosed herein. It is also obvious that when one pumpfails or operates in a pump-off condition, the pump in this disclosurewill advantageously function as a simplex pump, with either only theupper or lower pump chambers pumping fluid.

The proposed duplex pump design in which two pumps are arranged oneither side of the motor is also believed preferable to alternatedesigns in which the duplex pumps are mounted either completely above orcompletely below the motor. While such arrangements may potentiallyprovide a simpler mechanical interface between the motor and the pump,this is offset due to a more complicated design of the pumping chambersand the considerable complexity required in the design of flowing fluidpaths to achieve full duplex pumping.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example linear pumping system for pumping fluids froman oil or gas well in accordance with this disclosure.

FIGS. 2A, 2B, 2C, and 2D depict an example of the fluid pumping actionof the linear pumping system shown in FIG. 1.

FIG. 3 is a stroke-pressure diagram illustrating an example method ofoperating a linear pumping system to regulate pressure buildup withinthe pump chambers.

FIGS. 4A, 4B, and 4C are diagrams illustrating different types of linearmotors that can be used in different embodiments.

FIGS. 5A and 5B illustrate an embodiment of a linear motor with a moverand stator, and the mechanism to control the motion of a mover relativeto the stator.

FIGS. 6A, 6B, 6C, and 6D are a series of diagrams illustrating how thepump behavior can be determined from the piston pressure.

DETAILED DESCRIPTION

FIG. 1 depicts an example linear pumping system for pumping fluids froman oil or gas well. The left-hand portion 14 of FIG. 1 shows separatecomponents of a partially disassembled linear pumping system, and theright-hand portion 16 of FIG. 1 depicts a fully assembled pumpingsystem.

The example linear pumping system depicted in FIG. 1 includes a pumpcasing 11 that encloses a linear motor comprising stator 5 and mover 15,an upper pump 12 and a lower pump 6, such that the linear motor(including stator 5 and mover 15) is integrated into the pump assembly.The pump casing 11 includes an upper fluid inlet port 22, a lower fluidinlet port 23, and a fluid outlet port 1.

As noted, the linear motor includes a stator 5 and a mover 15. Thelinear motor mover 15 includes a plunger rod made of mechanically strongmaterial that is surrounded by permanent magnets 9 at a center portionof the rod, defining an upper plunger portion 8 extending above thepermanent magnets 9 and a lower plunger portion 19 extending below thepermanent magnets 9. In embodiments, the plunger rod of the linear motormay have a small diameter (e.g., less than one inch) to provide a pumpsystem that is suitable for use in deep wells at low flow rates and alsopumping fluid from a small diameter oil or gas well. A person of skillin the art will appreciate that the primary advantage of a small pump isthat it reduces the force the linear motor has to generate to move thepump plunger, which in turn makes the pump small and cheaper to build.In operation, the linear motor mover 15 is caused to move alternately upand down within the motor assembly when the stator 5 is coupled to apower source. The up and down movement of the linear motor mover 15within the linear motor assembly is respectively referred to herein asthe upstroke and downstroke of the linear motor.

In an embodiment, the linear motor may be an oil-filled motor assemblyto improve longevity and provide a highly efficient motor with closetolerances between the mover 15 and stator 5. Oil may be contained inthe motor assembly using pressure balancing diaphragms made from a softmaterial, such as silicone or an elastomer, to allow the oil to expandand contract with temperature. In the example illustrated in FIG. 1, oilis sealed within the motor assembly by moving seals 3, 17 that provideseals between the mover 15 and the upper and lower pump chambers 2, 13.The illustrated example further includes bellows 4, 18 that allow theoil to expand and contract with temperature within the motor chamber.

The upper and lower pumps (12 and 6, respectively) each include a fluidinlet valve 7, 10 and a fluid outlet valve 21, 20 respectively, and eachdefine a pump chamber 2 (upper) and 13 (lower) for receiving the upperand lower plunger rod portions 8, 19 of the linear motor mover 15.Specifically, the upper pump chamber 2 is configured to receive theupper plunger portion 8 and the lower pump chamber 13 is configured toreceive the lower plunger portion 19, as illustrated by the fullyassembled pump shown on the right-hand side 16 of FIG. 1. In this way, aduplex pump is formed with minimal complexity and size from two simplexpumps mounted on either end of the linear motor (stator 5 and mover 15),allowing fluid to be pumped in both stroking directions.

The fluid inlet (7, 10) and outlet (21, 20) valves to the upper andlower pump chambers 2, 13 are one-way valves (i.e., non-return valves),and are preferably configured to allow the linear pumping system tooperate in any orientation without being dependent on gravity.Specifically, the fluid inlet valves 7, 10 are one-way valves that arerespectively coupled between the upper and lower pump chambers 2, 13 andthe upper and lower fluid inlet ports at 22, 23, and are configured toreceive fluid into the pump chambers 2, 13 from outside of the pumpcasing 11. The fluid inlet valves 7, 10 may preferably be coupled tofluid inlet ports 22, 23 that are oriented such that the fluid inletsare not in line with the length of the pumping chamber, as shown in theillustrated embodiment. The fluid outlet valves 21, 20 are one-wayvalves that are respectively coupled between the upper and lower pumpchambers 2, 13 and an interior cavity 24 of the pump casing 11, and areconfigured to expel fluid from the pump chambers 2, 13 into the interiorcavity 24 of the pump casing. In an embodiment, the one-way inlet (7,10) and outlet (21, 20) valves may comprise buoyant balls in ball valvesthat are configured to move with the fluid without being dependent ongravity. The buoyant ball valves may, for example, utilize a retainingspring force provided by a spring return mechanism. In another example,the buoyant ball valves may include buoyant metallic balls (e.g., hollowmetal balls) and magnets in the ball seats to attract the balls backinto the valve seat. Other one-way valves known in the art may also beused, as appropriate.

In operation, on an upstroke of the linear motor mover 15, fluid isdrawn into the lower pump chamber 13 and expelled from the upper pumpchamber 2, and on a downstroke of the linear motor mover 15, fluid isdrawn into the upper pump chamber 2 and expelled from the lower pumpchamber 13. Fluid from both pump chambers 2, 13 is expelled into theinterior cavity 24 of the pump casing 11, and the resulting hydraulicpressure causes the fluid to be expelled through the fluid outlet port 1of the casing, for example into a fluid pipeline. The linear pump systemmay preferably be configured to operate in an oil or gas well at aminimum of 20 strokes per minute and a maximum of 1200 strokes perminute, such that the pump system may achieve reasonable flow rates withsmall diameter pumping chambers. An example of the fluid pumping actionof the linear pumping system is shown in the diagrams of FIG. 2.

The example illustrated in FIGS. 2A-2D depicts the operation of a linearpumping system in four stages, where certain reference numerals used inFIG. 1 have been omitted for clarity. The linear pumping system in theillustrated example is submersed within a fluid 25, such as oil. In thefirst stage (FIGS. 2A to 2B) of operation, a down stroke of the linearmotor causes a suction within the upper pump chamber 2 that draws fluidinto the upper pump chamber 2 through the upper fluid inlet port 22. Inthe second stage (FIGS. 2B to 2C) of operation, an upstroke of thelinear motor causes the fluid to be expelled from the upper pump chamber2 through the one-way fluid outlet valve 21 into an interior cavity 24of the pump casing. On the same upstroke of the linear motor in thesecond stage (FIGS. 2B to 2C) of operation, a suction is created in thelower pump chamber 13, drawing fluid into the lower pump chamber 13through the lower fluid inlet port 23.

In the third stage of operation (FIGS. 2C to 2D), the next down strokeof the linear motor causes fluid to refill the upper pump chamber 2 andfluid to be expelled from the lower pump chamber 13 through the one-wayfluid outlet valve 20 and into the interior cavity 24 of the pumpcasing. At the third stage of operation, fluid expelled from both theupper and lower pump chambers 2, 13 has intermixed within the interiorcavity 24 of the pump casing, and the resulting hydraulic pressurecauses fluid to exit the pump casing through the fluid outlet port 1.Similarly, in the fourth stage of operation (FIGS. 2C to 2D), the nextupstroke of the linear motor causes fluid to refill the lower pumpchamber 13, fluid to be expelled from the upper pump chamber 2 into theinterior cavity of the pump casing 24, and fluid to exit the pump casingthrough the fluid outlet port 1. The linear pumping system thencontinues to cycle between the third and fourth operational stages(FIGS. 2C, 2D), pumping fluid out of the pump casing from the fluidoutlet port 1 on each upstroke and down stroke of the linear motor.

In embodiments of the disclosure, the linear pumping system includes oneor more sensors (not shown here) that are configured to measure thelocation of the motor mover 15 within the motor assembly. Inembodiments, the linear pumping system may further include a motorcontroller (not illustrated) that is configured to regulate the movementand stroke of the pumping system based at least in part on the measuredlocation of the motor mover 15. In this way, the upper and lower plungerrod portions 8, 19 may be cycled to the end of their respective pumpchambers 2, 13, providing a maximum compression ratio for the pump.

In specific embodiments of the disclosure, the linear pumping system mayinclude one or more sensors (not shown) that are configured to measurethe pressure and/or temperature within the pump chambers 2, 13. Inembodiments, the linear pumping system may further include a motorcontroller (not shown) that is configured to regulate the movement andstroke of the pumping system based at least in part on the measuredpressure within the pump chambers 2, 13 in order to regulate pressure,e.g., to prevent the pump from becoming hydraulically locked. In thisway, the linear pumping system may provide full compression on gassyfluids and reduced compression on fluids.

FIG. 3 is a stroke-pressure diagram illustrating an example of how alinear pumping system may be controlled to regulate pressure buildupwithin the pump chambers. The diagram in FIG. 3 includes an example plotof measured pressure within a pump chamber during a cycle (i.e.,upstroke and downstroke) of the linear motor. The plotted solid line isan example of a normal pump cycle that includes a ramping portion 31where pressure is building within the chamber, followed by a flowingportion 33 (i.e., the horizontal flat portion) where fluid is pumped outof the chamber. If a pump outlet becomes blocked, however, then pressurewill continue to build within the pump chamber, as illustrated in FIG. 3by the continuation of the ramping pressure shown by the dotted line 32.By monitoring the pressure within the pump chamber, the pump movementmay be regulated to stop movement of the pump when the pressure reachesa predetermined threshold. In the illustrated example, pump movement isstopped at position 34 to prevent any further increase in pressure. Thepump may, for example, be regulated to stroke only to position 34 tomaintain the maximum possible pressure, or to stop under control of themotor controller. Details of the implementation control following thisprocessing operation are familiar to those of skill in the art and neednot be described in detail.

In another example, a feedback system similar to that shown in FIG. 3may be used to monitor and control the motor stator temperature. Thelinear motor may, for example, be stopped if the stator temperaturereaches a predetermined threshold, or may be regulated to slow the motoror cause the motor to operate with a reduced stroke to maintain thestator temperature below the predetermined threshold (i.e., the maximumoperating temperature.) Again, details of the practical implementationof such control need not be described in detail.

In yet additional embodiments, the linear pumping system may be furtherconfigured to measure or compute the amount of gas in the pump based onthe motor current and chamber pressures. In this way, the stroke lengthof the linear motor may be altered to better suit the fluid beingpumped, allowing the linear pumping system to operate effectively withfluids of different viscosities and with varying amounts of intermixedgas.

Linear motors can be implemented with a simple coils and metal structurewhere the induction of large currents in the mover creates movement, alinear induction motor. A linear motor can also be implemented with areluctance linear motor with several windings and an alternatingmagnetic mover so that moving the field along the length of the motorprovides movement of the mover. This implementation is a synchronouslinear reluctance motor. The third possibility is to incorporatepermanent magnets into the mover and/or stator increasing the fluxdensity and energy density of the motor, which is a synchronouspermanent magnet linear motor. FIGS. 4A-4C illustrate this principle.

In FIG. 4A, a linear induction motor is shown with active windings inthe stator 42 and a cylindrical solid metal mover 41. The motor is aninduction motor inducing high currents in the solid mover. In FIG. 4Bthe motor consists of a stator 44 with alternating magnetic propertiesand a stator 43 with alternating field coils. The field in the statorcoils is alternated to create a moving magnetic force which can bealternated to create linear motion, as illustrated in more detail in thefollowing FIG. 5B. The control and switching of the stator windings hasto be synchronized to the position of the mover, hence the termsynchronous motor can be used.

In FIG. 4C, the motor consists of a stator 46 with alternating magneticproperties (and in one embodiment permanent magnets) and a stator 45with alternating field coils, and permanent magnets. The field in thestator coils is alternated to create a moving magnetic force which canbe alternated to create linear motion. The control and switching of thestator windings has to be synchronized to the position of the mover,hence the term synchronous permanent magnet motor can be used.

The issue of the manner in which motion can be controlled in a linearoscillating motor as shown above has several important aspects. The mainareas of concern in controlling the motor motion is starting andcontrolling the stops and starts at the ends of the motion range.

FIG. 5A illustrates again a mover 15 and stator 5 in a specificembodiment. FIG. 5B provides a closer look at the magnetic system. Inparticular, as shown, the mover has several pairs of alternatingmagnetic elements 52 and 53 that make up the complete mover, while thestator has several alternating windings 50 and 51. It will beappreciated that in the above arrangement reversing the electrical fieldin windings 50 and 51 (and all the other stator windings) in anti-phaseresults in moving the mover in one direction or the other. To createcontinuous movement, the fields in windings 50 and 51 must remain in onepolarity until a pair of magnetic elements in the mover moves over thewindings pair. Once the pair of magnetic elements in the mover movespast the pair of windings, the fields in the stator windings must bereversed to then continue the movement to the next pair of stator fieldcoils. Reversing the fields again continues the movement of the mover15.

This principle of operation requires the stator fields to be reversed ata frequency dependent on the distance between the magnetic componentsand the linear speed of the motor. Accordingly, for this motor tooperate, the stator field coils must be switched at the correct point tocreate a moving field which is always creating motion in one direction.When the mover approaches the end of its stroke, the rate of fieldswitching should preferably be slowed to slow down the motion of themover, and also finally be applied out of phase to stop the motion.Preferably, the system will ramp down the linear mover velocity towardthe end of the stroke, bringing the mover to a halt a very smalldistance away from the end of the mechanical travel, without makingcontact with the end of the pump chamber. Such operation requiressensing of the position of the mover and in particular determining howclose the mover is to the end of the stroke.

Sensing of the mover position is therefore important in the control of alinear synchronous motor. There are several methods of control that canbe used in different embodiments. One simple control mechanism inapplications where the motor will operate a long way from the powersupply in a deep well, is to sense the current drawn by the statorcoils. This current is proportional to the relative position of themover magnetic circuit (whether passive, as in a reluctance motor oractive with a permanent magnet motor). Thus, by sensing the currentdrawn by the stator it is possible to establish where the mover isrelative to the stator. It is, however, problematic to determine howclose the mover is to the end of travel. One possible method ofestablishing this end of travel position is to switch fields slowly atstart up until the mover comes in contact with the end of the pumpchamber, at which point the stator coil current will increase rapidly,and the mover will not move. Once the end position is known, thecontroller can simply count the stator current changes as the movermoves through the stator windings. Since the size of the motor is knownand the number of coils is known, counting the current changes can beused as a position sensor.

In alternative embodiments, electronic position sensors may be fitted tothe motor so that its absolute position and velocity can be sensed realtime. This approach provides more accurate and direct feedback forcontrolling the motion of the mover. A person of skill in the art willappreciate details of the implementation of such control mechanisms,which are thus not discussed in further detail.

Controlling the motion of the mover in the manner described above isanother aspect of this invention. In particular, in this aspect thegeneral control mechanism which in its simplest form is used to createlinear oscillating motion of the mover relative to the stator, is alsofurther controlled to adapt the pump behavior to respond moreappropriately to changing fluid conditions in the pump. The mainadditional aspects of control include prevention of over pressure,adapting the motor speed to react to motor winding over temperature, anddealing with gassy fluids and gases.

Over pressure can happen because of stuck valves, or heavy fluids, deepwells, etc. To address such conditions, in a specific embodiment apressure sensor can be fitted to one or both of the pumping chambers.Data from this pressure sensor(s) can be used to regulate the motorvelocity and stop the motor short of the end position to prevent overpressure. Mechanisms to take into account pressure sensor data tocontrol the mover are described in more detail below.

In alternative embodiments, if the motor winding temperature is measuredor computed, this temperature can be regulated by simply shutting themotor off if it gets too hot, or slowed down to reduce the powerconsumption to a level where the temperature rise becomes stable.

Additionally, it will be appreciated that gassy fluids will causereduced pressure build up as the gas compresses with the stroking of thepump. This means that the pump and motor can move a lot faster duringthe compression stroke and only slow down again as the gas reaches theopening pressure of the non-return valve. With this understanding, inaccordance with another embodiment the velocity profile of the pump canbe changed to make it pump gassy fluids more effectively. Such a changecan be implemented in practice by measuring the pressure in the pumpingchamber or, where no pressure sensor is available, the current drawn bythe motor. At any given depth this current will be proportional to theforce developed, and so the force required to stroke the pump can becalculated from the motor current. It will also be appreciated that themotor current is also proportional to the depth of the pump and thefriction in the seals, which can also be taken into account for moreaccurate control.

Implementation details of these and other control mechanisms will beappreciated by those of skill in the art, and employed in practicalimplementations without departing from the principles of this invention.The following description is intended to provide additional detail andillustration.

FIG. 6A shows one of the two identical pumping sections in FIG. 1,illustrating that the pressure at the fluid inlet port 22 may bemeasured using a sensor 70. Pressure in the piston chamber 2 may also bemeasured using a second sensor. In different embodiments, the positionof the mover 8 can be measured using an additional down hole sensor 63,or computed at the surface.

FIG. 6B shows the pressure build up in the chamber with the pistonmoving during one stroke of the piston. In an upstroke of the piston,the fluid in the chamber is compressed, with the pressure building asthe velocity of the motor increases and the pressure rises to overcomethe tubing pressure, opening the upper valve. This portion of thediagram is illustrated by line 64. Then, as the valve opens, thepressure becomes steady at constant velocity, as illustrated by line 65.The pressure is directly proportional to force and so the motor currentwill also provide a measure of cylinder pressure, albeit also related toseveral other factors like friction and pump mover inertia. Accordingly,one can measure the activity in the pump chamber either directly withpressure sensors (such as 70), or indirectly via the motor current.

FIG. 6C illustrates a pump chamber with some fluid and some gas in it.This combination leads to a complex pressure stroke diagram withdifferent segments, such as 66, 67 and 68 illustrated in FIG. 6C,corresponding to different stages in the mover stroke and fluid-gascombinations. In particular, the initial pressure rise will be slow andthe piston will initially compress the gas, leading to a strokingpressure with the gas in compression and the incompressible fluidflowing. In the case of a complex fluid-gas mixture, the pressure strokeoverall diagram is likely to be complex as gas under pressure willlikely release rapidly through the exit valve.

FIG. 6D illustrates a chamber filled with gas, which will restrict thepressure achievable as the pump compresses the gas it may never generateenough pressure as shown by line 69 in FIG. 6D to open the valve, or itmay in the final portion of the pump stroke compress the gassufficiently to open the exit valve.

It is an intention of this invention that either using pressure sensorsand/or current measurement one can measure the pressure behavior in thepump chambers and determine the fluid and gas mix the pump is workingwith. Importantly, in accordance with an aspect of the invention,information about the fluid mix in the chamber can be used to adjust thepump control, so the piston movement suits the property of the mix.

Note that in the event the pump is immersed in gas only, this will alterthe pressure and current behavior as indicated above, but also reducethe cooling available to the motor, and accordingly would also result inincreased motor winding temperatures. The measurement of motortemperature is therefore a useful measurement, as well as the pressureto determine what fluid or gas mixture the pump is working in.

This application uses examples to illustrate the invention, the scope ofwhich is determined by the attached claims. Other examples fallingwithin the scope of the invention may be apparent to those of skill inthe art. It is noted that the figures described herein are notnecessarily to scale. Certain features of the instant disclosure may beshown exaggerated in scale or in somewhat schematic form, and somedetails of conventional elements may not be shown in the interest ofclarity and conciseness. It is to be recognized that the differentteachings of the embodiments discussed herein may be employed separatelyor in any suitable combination to produce the desired results.

What is claimed is:
 1. A linear pumping system, comprising: (a) a pumpcasing having an interior cavity and at least one fluid inlet portreceiving fluid from outside the pump casing, and at least one fluidoutlet port expelling fluid from the interior cavity to the outside ofthe pump casing; (b) a linear motor enclosed within the pump casing andincluding a stator and a mover, the mover including a plunger and beingconfigured to move alternately up and down with respect to the stator;and (c) a first pump enclosed within the pump casing and including afirst pump chamber, a first pump fluid inlet valve configured to receivefluid into the first pump chamber from outside the pump casing throughthe at least one fluid inlet port of the pump casing, and a first pumpfluid outlet valve configured to expel fluid from the first pump chamberinto the interior cavity of the pump casing, wherein the first pumpchamber is configured to receive a top portion of the plunger of thelinear motor mover, the received top plunger portion causing fluid to bedrawn into the first pump chamber through the first pump inlet valve ona downstroke of the linear motor mover, and causing fluid to be expelledfrom the first pump chamber into the interior cavity of the pump casingthrough the first pump outlet valve on an upstroke of the linear motormover; and wherein hydraulic pressure from the first pump causes fluidwithin the interior cavity of the pump casing to be expelled through thefluid outlet port of the pump casing.
 2. The linear pumping system ofclaim 1, further comprising (d) a second pump enclosed within the pumpcasing and including a second pump chamber, a second pump fluid inletvalve configured to receive fluid into the second pump chamber fromoutside the pump casing through the at least one fluid inlet port of thepump casing, and a second pump fluid outlet valve configured to expelfluid from the second pump chamber into the interior cavity of the pumpcasing, wherein the second pump chamber is configured to receive abottom portion of the plunger of the linear motor mover, the receivedbottom plunger portion causing fluid to be drawn into the second pumpchamber through the second pump inlet valve on an upstroke of the linearmotor mover, and causing fluid to be expelled from the second pumpchamber into the interior cavity of the pump casing through the secondpump outlet valve on a downstroke of the linear motor mover; and whereinhydraulic pressure from the first pump and the second pump causes fluidwithin the interior cavity of the pump casing to be expelled through thefluid outlet port of the pump casing.
 3. The linear pumping system ofclaim 1, wherein the linear motor further includes an expandablediaphragm that seals oil within the linear motor and is configured toallow the oil within the linear motor to expand or contract withtemperature.
 4. The linear pumping system of claim 2, wherein the firstand second pump fluid inlet valves and first and second pump fluidoutlet valves are one-way valves that are configured to operate in anyorientation.
 5. The linear pumping system of claim 4, wherein at leastone of the first and second pump fluid inlet valves and first and secondpump fluid outlet valves comprises a ball valve having a buoyant ball.6. The linear pumping system of claim 4, wherein at least one of thefirst and second pump fluid inlet valves and the first and second pumpoutlet valves comprises a ball valve having a metallic ball and amagnetic valve seat.
 7. The linear pumping system of claim 2, whereinthe first and second pump fluid inlet ports are configured to receivefluid in a direction that is substantially perpendicular to a lengthwisedirection of the first and second pump chambers.
 8. The linear pumpingsystem of claim 2, further comprising one or more pressure sensorsconfigured to measure pressure within at least one of the first andsecond pump chambers.
 9. The linear pumping system of claim 8, furthercomprising a motor controller that is configured to control movement ofthe linear motor based at least in part on pressure measured by the oneor more pressure sensors.
 10. The linear pumping system of claim 9,wherein the motor controller is configured to control one or more motionparameters of the linear motor dependent on the pressure measured withinat least one of the first or second pump chambers.
 11. The linearpumping system of claim 2, further comprising one or more sensorsconfigured to determine a location of the mover in relation to at leastone of the first and second pump chambers.
 12. The linear pumping systemof claim 11, further comprising a motor controller configured to controla stroke length of the linear motor based at least in part on theposition of the mover.
 13. The linear pumping system of claim 1, furthercomprising one or more temperature sensors configured to measure anoperating temperature of the linear motor.
 14. The linear pumping systemof claim 13, further comprising a motor controller that is configured tocontrol one or more motion parameters of the linear motor based at leastin part on the measured operating temperature of the linear motor. 15.The linear pumping system of claim 14, wherein the motor controller isconfigured to stop movement of the linear motor if the measuredoperating temperature of the linear motor reaches a predeterminedthreshold.
 16. A method of controlling operation of a linear pumpingsystem for use in an oil or gas well, the linear pumping systemincluding a linear motor and one or more pump chambers, comprising:measuring pressure within the one or more pump chambers of the linearpumping system; measuring a position of a plunger rod of the linearmotor in relation to the one or more pump chambers; and controllingmovement of the plunger rod within the one or more pump chambers basedat least in part on the measured pressure and position.
 17. The methodof claim 16, wherein a stroke length of the linear motor is controlledbased at least in part on the measured position to cause a maximumpenetration of the plunger rod within the one or more pump chambers. 18.The method of claim 16, wherein movement of the linear motor is stoppedif the measured pressure exceeds a predetermined threshold.
 19. Themethod of claim 16, further comprising: measuring an operationaltemperature of the linear motor; and controlling movement of the linearmotor based at least in part on the measured operational temperature.20. The method of claim 19, wherein movement of the linear motor isstopped if the measured operational temperature exceeds a predeterminedthreshold.
 21. The method of claim 16, further comprising the step ofusing at least one of (a) pressure measurements within the one or morepump chambers and (b) linear motor temperature to provide an estimate ofthe fluid/gas mixture in the portion of the oil or gas well where thelinear pumping system is located.